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Microsoft releases Azure Linux 4.0, a general-purpose Linux distribution, and Azure Container Linux

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Microsoft Launches Azure Linux 4.0: A General-Purpose Linux Distribution for the Cloud

At the Open Source Summit North America, Microsoft announced Azure Linux 4.0, marking a significant evolution of its in-house Linux distribution into a full-fledged, general-purpose operating system for virtual machines on Azure.

"Linux has become the majority operating system running on Azure over the past decade."
— Brendan Burns, Microsoft Corporate Vice President

The company also productized Flatcar Container Linux as Azure Container Linux, a hardened, immutable container host designed for security and reliability at scale.

Key Features of Azure Linux 4.0

  • Built on Fedora and delivered as open-source on GitHub
  • Purpose-built for Azure, integrating vertically into the Azure infrastructure
  • Server-centric design with no graphical desktop environment
  • Two-year lifecycle with monthly security patches and a clear upgrade path
  • Future availability as a Windows Subsystem for Linux (WSL) image for local development

Background and Evolution

Microsoft has a history of Linux-based operating systems, including Azure Sphere and CBL-Mariner, which was later renamed Azure Linux.

Azure Linux 3.0 was previously restricted to third-party customers via Azure Kubernetes Service (AKS). Version 4.0 opens the distribution to all Azure virtual machine users.

The announcement was originally scheduled for a later event but was revealed early.

Company Insights

Lachlan Everson, Microsoft principal program manager on Azure's open-source team, emphasized that the new distribution incorporates learnings from the Mariner heritage, offering a consistent experience across development and cloud environments.

Microsoft noted that more than two-thirds of customer cores in Azure now run Linux, reinforcing the company's ongoing commitment to open-source and Linux-based solutions.

What This Means

With Azure Linux 4.0 and Azure Container Linux, Microsoft is providing enterprises with a vertically integrated, open-source Linux experience—optimized for Azure, hardened for containers, and designed for both development and production workloads.